Anti-chipping recording disc, reading method and recording head

ABSTRACT

Information recording disk comprising a main recording track comprising one or more interruptions and/or changes of turn, this giving rise to non-sequential reading and therefore to information which is difficult to access. The copying of such a disk by conventional means becomes very difficult, and this will make it possible on the one hand to detect counterfeits by detecting the information and on the other hand to render any copy unusable.

[0001] The invention relates to a anti-piracy recording disk and aprocess for recording and reading such a disk. The invention isapplicable in particular in the field of optical disks andmagneto-optical disks.

[0002] Compact disks of the CD-ROM type and DVDs (Digital Video Disks)are used to disseminate all kinds of information (data, programs).Traditionally, these disks were not susceptible to data piracy sincetheir capacity was greater than that of most storage means on themarket. With the appearance on the one hand of high-capacity hard disks,and on the other hand of cheap CD-ROM etchers, this situation iscompletely altered. The duplicating of data is now within the scope ofsemi-professionals or even amateurs.

[0003] In the various recording media, from the hard disk to the opticaldisk and to the magnetic tape, the information is grouped into elementsgenerally called blocks. A table of contents allocating the blocks tothe various files is recorded somewhere on the same medium. For example,the blocks of a Digital Audio (DA) CD are allocated to each of therecorded pieces of music via this table of contents. Likewise, theblocks of a CD-ROM are each allocated to relevant computer files. Eachblock number contains a data set, the goal being for the set of dataretrieved to perfectly reproduce those which were recorded, the sameones at each access. Error correcting codes reduce the inevitable errorrate to an acceptable value for the relevant application.

[0004] In a conventional disk, the information is written sequentiallyon a spiral. The various addresses are arranged in a numerical order.The reading of the information is therefore carried out sequentially.The invention relates to a recording disk in which reading cannot becarried out in a sequential manner.

[0005] The invention provides a solution making it possible to detect arecording which has been copied fraudulently and even to render thisrecording unusable.

[0006] The invention therefore—relates to an information recording diskcomprising a main recording track recorded in a general manner in theform of a spiral comprising a plurality of segments of almost concentricturns, characterized in that the said main track comprises one or moreinterruptions and/or changes of turn and in that the addresses of theblocks and/or sectors are not arranged sequentially on the track.

[0007] The various objects and characteristics of the invention willbecome more clearly apparent in the description which follows and in theappended figures which represent:

[0008]FIG. 1, an example of a recording disk with two spiral recordingtracks according to the invention;

[0009]FIGS. 2a to 2 e, examples of switchpoints from the main track tothe secondary track;

[0010]FIG. 3, a example of the addressing of the main and secondarytracks;

[0011]FIG. 4, a reading head device making it possible to write twotracks onto a disk;

[0012]FIGS. 5a, 5 b, a variant embodiment according to the invention.

[0013] In an optical disk, conventionally, the information is written ona spiral-shaped track. The reader follows this spiral so as to recoverthe information. If it needs data which lies far from the point at whichthe optical head is located, it moves by a distance specified by theorigin position and the table of contents (TOC) and then makes a finesearch for the area requested by using the sector number informationread. According to the invention, at least one secondary track parallelto the main track, and which is therefore nested with the first, isintroduced into at least one area of the disk. Normally, when reading,the reader will be positioned on the main track or on a secondary trackin a random manner.

[0014] According to FIGS. 2a to 2 c, the secondary track Ps can bejoined up to the main track Pp by a “Y”-shaped switchpoint. In FIG. 2a,the switchpoint consists of a tracking element Y of large dimension. InFIG. 2b this element Y is wider at the branchpoint. In FIG. 2c, the maintrack Pp1 is interrupted and continues via the main track Pp2 which isslightly offset from the axis of the track Pp1. The secondary track Psis symmetric with Pp2 with respect to the axis of Pp1.

[0015] According to FIG. 2d, there is no symmetry between the secondarytrack and the main track. The main track, for example, has no change ofdirection and it is the secondary track which joins up with the maintrack.

[0016] The introduction of the random positioning may come from thedrawings of a bifurcation at a certain place on the track, the readerchoosing one or the other branch while reading depending on theinstantaneous state of the tracking signal.

[0017] According to FIG. 2e, there is no join between the main track andthe secondary track; the latter is simply placed in parallel with themain track.

[0018] The reading manager of the reader will be responsible for readingboth the secondary track and the main track. This will be explained ingreater detail as the description proceeds.

[0019] According to the invention, provision is also made to writedifferent data to the secondary track and to the main track. Under theseconditions, it will be easy to recognize an original disk and a copieddisk.

[0020] This is because the act of copying the disk does not make itpossible to duplicate both the secondary track and the main track. Thecopying system takes into account one and only one set of data.Moreover, even if a computer specialist who has understood the devicereads the coded sector a great many times so as to obtain access to thetwo sets of information, he does not have a device capable ofreproducing the random behaviour alluded to.

[0021] Moreover, not only will it be possible to detect a copy of such adisk, but by providing, on the secondary track, data necessary for theoperation of the software of the disk, it is possible to render such acopy unusable.

[0022] For the management of such a disk, provision may be made for thesecondary track to contain one or more information blocks. Thestart-of-block address may be equal to a start-of-block address situatedon a main track which neighbours it. More precisely, it may be situatedsubstantially on the same radius of the disk.

[0023] According to another variant, the secondary track contains blockswhose addresses are not contained on the main track. To read thesuccessive blocks of the disk, therefore, the blocks of the secondarytrack will have to be read.

[0024] By providing one or more secondary tracks nested in the spiral ofthe main track, the disk of the invention may not be reproduced in fulland makes it possible to render “pirate” copies detectable or even torender them unusable.

[0025] According to another variant, the disk comprises at least onearea with a large number of discontinuous or continuous segments oftracks, which may be entwined. An example of this configuration isdepicted in FIG. 5a. By way of example, the CD-ROM consists of nearly300,000 blocks of 2 kbytes. The modified area can comprise a number ofbifurcations of the order of magnitude of the number of blocks, that isto say each block can be followed by a continuation (straight on, to theright or to the left) or by an interruption of the groove.

[0026] Analysis of this modified area with the aid of an optical readertype device can take a very long time and even be countered by the poorpositioning and repetition of the block numbers. For example, the tracksegments may contain block addresses which are not strictly in the orderof their physical position, contrary to the usual rule. Additionally,the field required to trace back to the topography of the sectors on thedisk is such that it is almost impossible to access the topography ofthe disk by optical means.

[0027] Only information on the topography of the disk in accordance withthe invention makes it possible to access all the segments, and henceall the information.

[0028] To manufacture such a disk, two or three beams can write (or not)spiral tracks in parallel. In order to preserve the normal operation ofdisk readers, the pitch of the two spirals can be increased so as topreserve a spacing equal to that imposed by the standard rules (1.6 μmfor CD-ROMs, 0.65 μm for the first generation DVDs).

[0029] The machines used at present to manufacture masters etch just asingle groove while the disk is rotating, the beam moving radiallysynchronously with the rotation. A modification of these machines formanufacturing masters is therefore necessary. On the one hand, thevariable pitch of the various spirals necessitates controlling theradial movement of the etching laser with a time-varying speed. On theother hand, an acousto-optical component serving to modulate the beamcan be used with two or three frequencies which are different butsufficiently close together to be controlled from a conventionalelectronic circuit. The separation of the two directions and of the zeroorder also entails a modification of the focusing optics. FIG. 4provides, in a simplified manner, such a system in which anacousto-optical transducer AO receiving a laser beam modulates it withtwo frequencies f1 and f2 or more. Two angularly deviated beams thenmake it possible to etch two tracks either simultaneously orsubsequently so as to make one or two parallel tracks. The undeflectedbeam (order 0) is blocked by the mask M.

[0030] Between the acousto-optical transducer AO is provided a device Lwhich focuses the beams onto the disk. Moreover, this device cancomprise means for blocking the transmission of the beam of ordertransmitted by the acousto-optical device AO.

[0031] The reading of such a disk possessing at least one secondarytrack will now be described.

[0032] Firstly let us consider the case in which the secondary track isnested in the spiral of the main track as is represented in FIG. 1 andthat the block numbers (or physical addresses) of this secondary trackare different from those of the main track.

[0033] If it is assumed that the physical address n is given to a blockof the secondary track and to a block of the main track, when thereading system requests that this address n be read, according to thecurrent operation of readers, a fast search is carried out by readingthe block numbers and then by a finer search, for example by countingthe tracks traversed, followed possibly by corrections until therelevant block n is detected. The fast positioning, and to some extentthe slower positioning, is random to within a track. This can beexploited if the double spiral extends far enough around the address nto reach the most probable landing area of the reading system.

[0034] However, since an address n is located both on the secondarytrack and on the main track according to whether during the search thedisk reading head moves from the centre of the disk to the periphery orvice versa, it will first find either the address n of the secondarytrack, or the address n of the main track. The reading system cantherefore be programmed in such a way that in the search for types ofaddresses which exist twice in the disk, two searches are made: onesearch with a movement of the reading head from the centre of the disktowards the periphery and one search from the periphery of the disktowards the centre. Thus, the two addresses n will necessarily bereached and it will be possible to read the blocks situated at theseaddresses.

[0035] Another method also consists in reading the address n+i of themain track close to the area n, then the address n. Next, reading theaddress n−i of the main track also close to the area n, then the addressn. In this way, if the secondary track is short (less than onerevolution of the disk), both addresses n of the secondary track and ofthe main track will be reached.

[0036] The reading of main and secondary tracks possessing a branchpointsuch as that represented in FIGS. 2a to 2 c will now be described.

[0037] Let us assume that at a given point a main track splits into twodaughter tracks (a main track and a secondary track). A priori, eachparticular system will veer either to one side, or to the otherrepetitively. However, for each system, a particular geometry willinduce a random orientation between the branches. A limited number ofbranchpoint geometries makes it possible to obtain the “random” geometryof most of the systems on the market.

[0038] In order to limit the disturbance to the system on passing thebranchpoint, it is easy to write the same data in a perfectlysynchronous manner on both branches as long as the latter are closetogether.

[0039] If it is decided to intervene in a fine manner in the operationof the reader, it is possible to introduce a slight bias into thetracking actuator with each pass in one direction and in the othersuccessively so as to aid orientation onto one branch or the other.

[0040] In any event, an almost certain way of reading the two addressesn situated on the secondary track and on the main track is to read thedata situated at these addresses several times, record them and comparethem. If it is observed that different data have been read at twoaddresses n, it may be deduced from this that the secondary track andthe main track have been read.

[0041] Finally, the case will now be explained of the reading of asecondary track whose addresses or addresses of blocks does not exist onthe main track.

[0042] This case is represented by FIG. 3.

[0043] Let us assume that at least locally a disk supports two nestedspirals. The main track carries on one revolution, for example, thecontiguous addresses from n to n+i, then on a second revolution fromn+2i+1 to n+3i etc. The secondary track carries the addresses from n+i+1to n+2i in such a way that this section is “sandwiched” between the tworelevant sections of the main track. The software examines the behaviourof the reading head when reading the three series of addresses. Thetrack jumps are characteristic of the layout of the blocks; inparticular, if a reading of blocks n to n+3i is requested, the fineand/or coarse tracking signal carry the signature of the two jumpsrequired to recover all the blocks.

[0044] The disk of the invention makes it possible to introduce arandomness when reading data on a disk recorded in accordance with theinvention. For example, any reader on the market, when the programcommands it to read the particular sector of the disk coded inaccordance with the method proposed, will sometimes read one data set Aand sometimes another set B.

[0045] However, this CD or DVD disk, copied by conventional, evensophisticated, means will contain a single data set. By attempting anumber of accesses to the relevant sector, the program will then be ableto determine, if the data reread are always the same, that the disk is acopy; if they are sometimes A and sometimes B, that the disk is anoriginal.

[0046] The benefit of this design of disk is that it is compatible withall the existing CD-ROM readers on the market without even needing tomodify their software operation (Driver).

[0047] In the alternative embodiment of FIGS. 5a and 5 b the track Pp isregarded as being the main track and information is regarded as beingwritten on secondary tracks Ps1, . . . Psn. The track Psn is regardedfor example as representing a sector (or a block) and as containing ablock with address A such that this sector should be located on thetrack Ps1. Block A should therefore be regarded as having been moved andas not being in its logical place. The disk's normal reading system willtherefore be incapable of retrieving this sector. To alleviate thisproblem, the invention makes provision in various neighbouring tracks towrite information making it possible to find the address A. For example,the track Ps1 contains the address A and associated with this address,an information item a1 indicating that in jump of 3 tracks be madetowards the outside of the disk to find the address A; the track Ps2also contains the address A and an information item a2 indicating that ajump of 2 tracks be made towards the outside of the disk; . . . thetrack Psn+2 contains the address A and an information item a5 indicatingthat a jump of 2 tracks be made towards the inside of the disk.Therefore, according to the invention, the information items a1, a2, . .. a5 contain positioning information giving the path to be followed soas to find the segment to be read. This information may be likened to“mechanical” information as opposed to logical information.

[0048] In the description of FIG. 5a, the track Pp was regarded as beinga main track and the other tracks as secondary tracks. It is alsopossible to regard all the tracks as being main tracks. In any event,the system is devised in such a way that the tracks contained in a ringencompassing a track containing a block with addresses such as Acomprises information for controlling the reading head, such as theabove information a1, a2, . . . a5.

[0049] We shall describe the operation of such a disk comprising a largenumber of track segments, in accordance with the invention:

[0050] As specified above, it is necessary to obtain information aboutthe topography of the disk in order to access the information. Thelatter may be present on an area of the disk in order to access theinformation. The latter may be present on an area of the disk, forexample in a coded manner. This information may also be dispersed overthe whole of the modified area.

[0051] An optical device of the Compact Disk reader type for exampleuses means for the coarse positioning of the reading head andelectromechanical and/or electrooptical means for tracking and forjumping tracks ensure the exact positioning of the reading spot on thetrack segment to be read.

[0052] When searching for information on the disk in accordance with theinvention, the pick-up is sent by the coarse operation to an areacomprising a large number of track fractions. It is not possibleaccurately to ascertain the position of the pick-up on the disk; on theother hand, the track segment reread contains user information and alsopositioning information giving the path (for example the number of trackjumps and their direction) for reaching the information carried on oneor more track segments located nearby. This information about the pathto be followed is specific to the segment reread. Accordingly, areasonable number of accesses does not make it possible to trace back toa complete map of the disk, the first step towards the illicit copyingof the contents.

[0053] On the other hand, access to an item of information of interestto the user on the disk in accordance with the innovation is effected ina time substantially equal to the access time in a conventional disk.

[0054] This design of disk therefore makes it possible to identify anoriginal disk and a disk copied by a pirate, even equipped withconsiderable means.

[0055] It does not involve any “dongle” type key, nor code, norinteraction between the supplier and the customer.

[0056] The reading of such a disk is compatible with the mechanicaloptical and electrical operation of CD.ROM readers, it may on the otherhand be necessary to modify the software operation (driver).

1. Information recording disk comprising a main recording track recordedin a general manner in the form of a spiral comprising a plurality ofsegments of almost concentric turns, characterized in that the said maintrack comprises one or more interruptions and/or changes of turn givingrise to one or more secondary tracks and in that the addresses of theblocks and/or sectors are not arranged sequentially on a single track.2. Disk according to claim 1, characterized in that the interruptionsand/or changes of turn give rise to one or more secondary tracks. 3.Disk according to claim 1, characterized in that the main track and thesecondary track or tracks comprise information situated in the sameangular sector of the disk.
 4. Disk according to claim 1, characterizedin that in the same angular sector, the neighbouring tracks of asecondary track as well as this secondary track contain information. 5.Disk according to one of claims 3 and 4, characterized in that specifiedsectors of the track contain positioning information making it possibleto access a block or sector moved with respect to its normal place onthe disk.
 6. Disk according to claim 1, characterized in that thesegments of turns constituting a ring incorporating a segment of turn inwhich a block with a specified address (A) is located each contain thesaid address with which is associated an information item forcontrolling a disk reading head.
 7. Disk according to claim 6,characterized in that a positioning information item associated with anaddress of a specified block or sector and contained in a segment oftrack comprises an indication representing the number of tracksseparating the said segment of track from the segment of track in whichthe said specified block or sector is localized.
 8. Disk according toclaim 7, characterized in that the positioning information item is atrack jump information item making it possible to instruct the diskreading head to move.
 9. Disk according to one of claims 2 and 3,characterized in that it comprises a secondary information trackparallel to the main information track.
 10. Disk according to claim 9,characterized in that the secondary track is shorter than the maintrack.
 11. Disk according to claim 9, characterized in that theadditional track is linked to the main track by a “Y”-shapedswitchpoint.
 12. Disk according to claim 8, characterized in that thesecondary track contains different information from that of the maintrack.
 13. Disk according to claim 7, characterized in that the addressof the start of the secondary track has the same address as a block ofthe main track.
 14. Disk according to claim 9, characterized in that thesecondary track has a length less than one revolution of the spiral ofthe track.
 15. Disk according to claim 9, characterized in that theaddresses of the data situated on the secondary track are different fromthose of the main track.
 16. Disk according to claim 9, characterized inthat the addresses of the data situated on the secondary trackcorrespond to unused addresses on the main track.
 17. Disk according toclaim 1, characterized in that the main track is in the form of aspiral, the pitch of whose tracks is variable in such a way as toprovide a larger pitch in the area intended to contain a secondarytrack.
 18. Process for reading a disk according to claim 9,characterized in that provision is made to search for an address nexisting both on the secondary track and on the main track by effectinga first search by moving the reading head from the centre of the disktowards the periphery and a second search by moving the reading headfrom the periphery towards the centre of the disk.
 19. Reading processaccording to claim 18, characterized in that, during a first step, asearch is made for the address (n−i) situated on a turn of the maintrack situated between the address n and the centre of the disk, then asearch is made for the address n, then during a second step, a search ismade for the address (n+i) situated on a turn of the main track situatedbetween the address n and the periphery of the disk, and then the searchis made for the address n.
 20. Process for reading a disk according toclaim 1, characterized in that several reads are performed on the datasituated at addresses (n) located on the secondary track and on the maintrack and in that the data read are recorded until the reading ofdifferent data is detected.
 21. Process for reading a disk according toclaim 11, characterized in that the reading head is caused to track insuch a way as to favour in a first step orientation towards one branchof the switchpoint, and then in a second step orientation towards theother branch of the switchpoint.
 22. Reading head for recording diskcharacterized in that it comprises an acousto-optical transducer placedin the path of a reading beam, the transducer being excited by twoacoustic waves at different frequencies (f1, f2) in such a way as toproduce at least two modulated writing beams.
 23. Reading head accordingto claim 22, characterized in that the said transducer makes it possibleto write at least two parallel information tracks.